In the last two decades, minimally invasive surgery (MIS) has reduced the trauma of surgery, speeded recovery times, and significantly reduced the cost of many surgical procedures. MIS has been greatly advanced by the growing miniaturization of medical technology. Using small incisions, and by introducing endoscopes or catheters with miniaturized sensors and tools at their tips, it is often possible to visualize, diagnose, and correct medical conditions that previously required major surgical intervention. A major obstacle to further advances in minimally invasive surgery, however, is the need to push catheters and endoscopes into the tortuous vessels, passageways and cavities of the body. Pushing a flexible instrument such as an endoscope risks buckling and damage to the device. More important, however, pushing an endoscope or catheter into the body risks perforating or otherwise damaging tissue, and can be extremely uncomfortable for the patient. For example, there is currently a controversy over use of sigmoidoscopy or colonoscopy to routinely to monitor and prevent colon cancer. Although colonoscopy provides a physician with a superior view of the entire colon, it is an invasive and difficult procedure requiring the colonoscope to be pushed around the right angle bends in the colon, and it requires anesthesia to reduce patient discomfort. Endoscopes and catheters could be further improved if they could pull themselves forward, rather than having to be pushed into position, and if they could bend regionally along their length as well as at their tips. Such devices could be further enhanced if they could sense local conditions and reflexively alter the propulsive force and/or direction.
It has been suggested to implement an autonomous catheter using localized vacuum and a bellows-like expansion and contraction to move itself through tubes and excised segments of porcine intestine. See Asari, V. K., S. Kumar, and I. Kassim, A fully autonomous microrobotic endoscopy system. J Intel Robot Sys, 2000. 28: p. 325-341. As understood, however, the center of this device may not be hollow.
Furthermore, studies of this device indicate that the vacuum clamp used to anchor the device before its center is extended by a bellows may be somewhat ineffective in dealing with changing colon diameters. Other known devices include a disposable ingestible capsule that can provide physicians with images of the gastro-intestinal tract and location information. A brief description of this device was published by Iddan, G., Meron, G., Glukhovsky, A., and Swain, P. in xe2x80x9cWireless capsule endoscopy,xe2x80x9d Nature 405:417, 2000. Because this device is moved entirely through the peristaltic action of the patient""s gastrointestinal system, however, it does not allow a physician to direct it or move it backwards.
Hence, there remains a need for a self-propelled device (i.e., not needing to be to be pushed) that provides a physician full control over the position of an endoscope or catheter. It would also be advantageous if such a device had certain reflexive capabilities that allowed a physician to utilize the device with greater ease. For example, if an endoscope could make reflexive adjustments in force, it would greatly facilitate a physician""s ability to guide and oversee effective surgeries and other procedures.
Endoscopes, catheters, and miniaturized tools with these capabilities could offer a wide variety of useful applications. A device could pull itself into the coronary arteries, and then scrape and suction away atherosclerotic plaque, stopping if it encountered a vessel wall. Another device of similar design could pull itself through the colon, and scrape and suction away precancerous polyps. Another device with these capabilities could pull itself into an artery of the brain, and scrape and suction away a clot. Moreover, such devices could have countless non-medical applications. For example, maintenance of traps and other complex plumbing in domestic and industrial settings currently relies either on pushing a passive device through an obstruction (e.g., a plumber""s snake) or chemically dissolving an obstruction. A self-propelled device able to negotiate intricate bends and other pathways could actively move towards an obstruction and apply small amounts of chemical to dissolve the obstruction, suck out material, or (if equipped with an appropriate manipulator) actively remove the material in the obstruction. Countless other possibilities exist.
Mechanical principles helpful in achieving these ends can be observed in hydrostatic animals such as worms or leeches. These organisms can insinuate themselves into highly curved and tortuous spaces. For example, the flatworm Schistosoma can successfully locomote into and anchor itself within human blood vessels. The tapeworm can locomote through and anchor itself within the human intestine. To date, however, there have only been limited attempts to adapt certain mechanical characteristics of these types of organisms to a self-propelled endoscope, catheter or similar device.
U.S. Pat. No. 5,662,587 discloses a robot that can propel itself through a body cavity by a combination of xe2x80x9ctractionxe2x80x9d and xe2x80x9cextension.xe2x80x9d A module enlarges by inflating a balloon or extending gripping arms, and another module either contracts or extends so as to pull (or push) the device along. In one arrangement, the ""587 patent also discloses concentric bellows in the same module. However, the ""587 patent still requires separate (and often complicated) mechanisms for performing the traction and extension functions. Thus, a need remains for a less intricate self-propelled robotic endoscope.
Accordingly, it is an object of this invention to provide a less complicated self-propelled device that can pull itself through tight passageways, such as may be found in the human body, without causing damage to surrounding tissue or structures. It is a further object of the invention to provide reflexive capabilities and control in such a device. Additional objects of the invention are described herein or will be apparent to those skilled in the art.
The invention comprises a self-propelled device capable of peristaltic locomotion, as well as other modes of locomotion. Peristaltic locomotion is caused by one or more actuators that surround a central flexible tube or other conduit. The device is thus able to move itself through a lumen, cavity or other area that might otherwise be inaccessible, and at the same time provide a conduit by which electrical control lines, fiber optic cables, fluid delivery tubes or other components can be extended into the region to which the device has moved itself.
In one embodiment, an actuator comprises an expandable bladder that surrounds a longitudinal section of the central tube and is fluid-impermeable at either end of that section. At least one end of the bladder is able to move toward the other end of the bladder along the central tube. Surrounding the bladder is a mesh of substantially inextensible fibers. As fluid is introduced into the region between the bladder""s inner wall and the central tube""s outer wall, the bladder expands. The mesh maintains the surface area of the bladder substantially constant, thereby causing at least one of the bladder""s ends to move towards the other end as the bladder expands outward radially from the central tube""s longitudinal axis. In this manner, a device according to the invention is able to expand laterally and contract longitudinally using a minimum number of moving parts. A restorative spring can be placed inside the bladder and between the two ends to restore the actuator to its original shape as fluid is withdrawn from the bladder. Multiple actuators can be placed in series to successively inflate and deflate. Through such successive inflation and deflation, a peristaltic motion results.
The actuator can also have one or more Shape Memory Alloy (SMA) springs affixed to the restorative spring. As an electric current is applied to the SMA spring, it contracts. The actuator thereby bends along the side of the SMA spring. The actuators can also be equipped with sensors to provide feedback for control purposes, as well as for therapeutic and diagnostic purposes.